1. Field of the Invention
The present invention relates to cylinder apparatus such as a hydraulic shock absorber, a hydraulic cylinder, etc. for use in a suspension system of an automobile, for example.
2. Description of Related Art
As an example of cylinder apparatus, a common cylinder-type hydraulic shock absorber attached to a suspension system of an automobile will be explained below. As disclosed in Japanese Patent Application Publication No. 2004-116711, for example, a cylinder-type hydraulic shock absorber includes a cylinder having a hydraulic fluid sealed therein. A piston is slidably fitted in the cylinder. The piston has a piston rod connected thereto to form a piston assembly. The piston assembly is provided with a damping force generating mechanism including an orifice, a disk valve, etc. The flow of hydraulic fluid induced by extension and contraction of the piston rod is controlled by the damping force generating mechanism, thereby generating damping force. The hydraulic shock absorber further includes a protecting cover in the shape of a circular cylinder, one end of which is closed. The protecting cover is secured to the piston rod to cover it and the cylinder.
In the hydraulic shock absorber of the above-mentioned JP Application Publication, a protecting cover made of a synthetic resin material is used from the viewpoint of weight saving. A metallic head cap formed in the shape of a circular cylinder, one end of which is closed, by deep drawing process or the like, is welded to the piston rod, and the synthetic resin protecting cover is press-fitted to the head cap so as to be secured thereto by the elasticity of the material thereof. At this time, the protecting cover elastically clamps a side surface portion of the head cap, thereby preventing the protecting cover from tilting relative to the piston rod. Thus, the protecting cover can be stably secured to the piston rod.
The hydraulic shock absorber disclosed in the JP Application Publication suffers, however, from the following problems. It is necessary in order to stably secure the protecting cover to the piston rod to provide a sufficiently long axial dimension for the side surface portion of the head cap that is clamped by the protecting cover. Therefore, the weight of the head cap increases. Further, the production cost increases because the head cap is formed by deep drawing process.